The present invention relates to firearms, and more particularly to firearms having a tubular magazine wherein a plurality of shotgun shells are loaded into the magazine tube for automatically feeding to the receiver. Specifically, the invention relates to an improved means for retaining the magazine spring within the tubular magazine in spring bias against the column of shotgun shells in the loaded magazine when the cap is removed, and also for detenting the magazine cap so as to prevent it from coming loose during normal use.
Certain shoulder firearms such as repeating shot-guns include tubular magazines secured to the forward end of the receiver. The magazine tube is commonly enclosed within the fore-end of a removable stock, usually made of wood. Shotgun shells are loaded into a magazine tube and are spring biased toward the receiver so as to permit automatic reloading after firing. The forward end of the magazine tube is closed by a cap threaded thereon. This cap also constitutes the forward abutment for the fore-end stock so that a tightly threaded cap will securely maintain the fore-end stock in place.
During normal use, the actions of the barrel recoil upon firing, ejection of the fired shell and subsequent reload tend to loosen the magazine cap. Without some detent mechanism, the cap will come completely off, thereby causing the spring and associated parts within the magazine tube to be expelled forward accidentally.
Several types of detent systems have been used in the past to prevent loosening of the magazine cap. One is described in U.S. Pat. No. 2,402,086 to Leon A. Rix, assigned to the assignee of the present invention, wherein the fore-end of the tube has a bushing brazed thereon provided with a circumferential series of ratchet teeth. A separate detent washer with a circumferential series of ratchet teeth is biased by the magazine spring against the inner end of the bushing so as to mesh with its ratchet teeth. The detent washer is provided with a protrusion which is intended to fit into a slot in the magazine cap so that, as the cap is tightened, the slot will engage the projection. Further tightening of the cap causes the teeth of the detent washer to engage those of the bushing until they are in fully seated meshing engagement. The cap is thus resiliently held against turning relative to the magazine tube.
Another prior art detent system is the subject of U.S. Pat. No. 4,087,930 to William H. Grehl, in which the magazine spring urges two projecting prongs or fingers of a detent member at the fore-end of the magazine tube into engagement with a slotted or notched surface along the inner periphery of the magazine cap. In this system, the spring retainer is a separate element from the detent member and the former must be friction fit to the wall of the magazine tube.
In yet another prior art detent system, a single detent is located along the circumference of a metal frame located within the fore-end stock. The detent is biased by its own spring to engage slots along the outer periphery of the magazine cap and thus detent the latter. This detent system is currently used on automatic shotguns manufactured by the assignee of the present invention under the designation "Model 1100" series.
The foregoing prior art systems, while accomplishing to some extent their purpose in keeping the magazine cap from unscrewing accidentally, suffer from several disadvantages. The Rix detent system is rather complex, requiring brazed bushings and constructed so that the magazine spring cannot be removed from cleaning when the cap is removed. Grehl requires a separate spring retainer which is friction fit to the wall of the magazine tube and is therefore difficult to get out. And the last-mentioned detent system requires a separate spring for the detent and a separate retainer for the magazine spring. It also does not permit substitution of more desirable and ligher weight aluminum caps in place of steel caps since the detent system tends to damage the former.